The otolith organs are known to provide ambiguous sensory cues, since like all linear accelerometers they respond both to gravity and linear acceleration (i.e., Einstein's Equivalence Principle). The long-term goals of this project are to understand how the nervous system uses sensory and non-sensory information to resolve the inherent ambiguity measured by the otolith organs. It is particularly crucial to understand these sensory interactions as we develop clinical procedures to assess otolith function, since responses to all otolith signals depend upon other cues, both sensory and non-sensory, because of the inherent otolith measurement ambiguity. From both personal knowledge of our own perceptions as well as scientific investigations of tilt and translation, we know that humans perceive both tilt, (i.e., relative orientation of gravity), and translation (i.e., linear acceleration). This clearly shows the human nervous system separates the ambiguous measurement of gravito-inertial force into separate, though possibly related, representations of tilt (gravity) and translation (linear acceleration). These (or similar) neural processes may also affect reflexive eye movements responses. We know that rotational cues from the canals influence both tilt and translation responses, and we also know that both visual motion and orientation cues influence both tilt and translation responses. But we do not thoroughly understand how other sensory and non-sensory influences might affect the processing of the otolith cues. Investigating other sensory and non-sensory influences is the short-term goal of our proposed research. To accomplish this short-term goal, we propose to investigate 3 specific aims. 1) Investigate VOR and roll tilt perception in non-human primates. 2) Investigate how the influence of canal cues on tilt and translation responses adapts. 3) Investigate the influence of efferent copy and neck receptor cues on the neural processes by which ambiguous otolith cues yield tilt and/or translation responses.